Not Applicable
Not Applicable
1. Field of the Invention
The present invention relates generally to the art of investment casting and more specifically to a method and apparatus for combining a conforming gas permeable mold within a correspondingly suitable vacuum chamber in a manner that subjects said mold to vacuum pressure while molten metal is introduced by gravity means from outside the vacuum chamber.
2. Description of the Related Art
The basic principles and methodogoly of investment or xe2x80x9clost waxxe2x80x9d casting have remained basically the same during the 6000 years it has been practiced. Investing a disposable pattern in a mold, eliminating the disposable pattern by burning it out, and introducing molten metal into the resultant mold cavity has never changed other than the quality of materials and equipment technology employed in the process. However, there have been many improvements made in the art during the time it has been known. Among the most important developments in modern times include the discovery that vacuum pressures applied to a gas permeable mold while molten metal is added will greatly enhance the fill out probabilities of complex shapes which otherwise depend entirely on sprue weight, elaborate conduits, venting gates, and hydrostatic pressures to completely fill out a complex mold.
Major changes in recent years have advanced vacuum assisted casting to the point where it is now standard practice to produce very complex articles, including highly detailed finished parts that require no additional machining, expensive assembly procedures, or further finishing of the cast article beyond sprue removal. Prior art examples include a wide variety of vacuum casting methods and equipment, which have proven to be successful in their intended applications. However, of the various processes heretofore used or proposed for use, few have received commercial consideration for high production industrial applications involving the precision casting of large and complex articles. The inherent fragility of large gas permeable molds such as ceramic shell molds hinder the progress towards utilizing vacuum casting for a broader range of casting applications. The method and apparatus comprising the present invention provide the combined benefits and advantages of ceramic shell molds with an ability to more economically produce larger, and more detailed precision castings requiring only minimum rework for manufacturing a finished product.
Therefore it is the primary objective of the present invention to reinforce and strengthen ceramic shell molds in a manner that makes them self-supporting, and to provide a uniform means for said molds to be mounted and sealed within a vacuum chamber regardless of mold size, shape, or mold type used, up to the size limitations of the particular vacuum chamber used in the process. The invention further permits molten metal to be introduced by gravity means from outside the vacuum chamber while said mold remains subjected to vacuum pressure.
It is another object of the invention to provide a method and apparatus that more efficiently drains melted pattern material from the mold during the pattern elimination process resulting in a cleaner mold at the beginning of the burnout phase, consequently reducing exposure to smoke and pollution in the workplace and to reduce undesirable emissions into the atmosphere.
It is still another object of the invention to provide a method and apparatus that furnishes a means for handling sprued patterns and finished molds safely to lessen the chance of damage while investing, drying, and setting up the mold for casting. Other related objectives and advantages are:
(a) To provide an improved method and apparatus that increases yield of the metal being cast by reducing the amount of metal that must be cut off the cast article in the form of sprues, gates, and risers.
(b) To provide an improved method and apparatus that allows thinner walled castings to be cast resulting in lighter finished articles and consequently less costly articles.
(c) To provide an improved method and apparatus that is applicable to the casting of a wide variety of different metals, including both ferrous and nonferrous metals.
(d) To provide an improved method and apparatus that permits the casting of articles of varying sizes and shapes one after the other in any desired order on a single production line thereby speeding up production and reducing costs.
(e) To provide an improved method and apparatus that can be used to sprue and cast any number of articles of any given configuration within a single mold up to the size limitations of the vacuum casting unit being used.
(f) To provide an improved method and apparatus that is capable of use with a variety of different casting designs involving different types of casting molds such as poured investment molds, ceramic shell molds, multiple mold sections, inserts, disintegrable cores, and the like.
(g) To provide an improved method and apparatus that can be used to cast different mold types one after the other in any desired order.
(h) To provide an improved method and apparatus that requires fewer production man-hours to be expended due to the high quality and precise detail of the cast articles.
(i) To provide an improved method and apparatus that is adaptable to high production output by combining any desired number of vacuum casting chambers in successive order such as a carousel arrangement or the like.
(j) To provide an improved method and apparatus that is reasonably simple and safe enough for use in a home workshop or teaching facility as well as a commercial foundry and is versatile enough for smaller units to be transported and used at any convenient site such as demonstration workshops or the like.
(k) To provide an improved apparatus that has a long operating life and minimal maintenance requirements.
(l) To provide an improved apparatus that accommodates any size, type, or shape of gas permeable mold in random or any desired order up to the maximum size of the vacuum casting unit used.
(m) To provide a method and apparatus suitable for space manufacturing projects utilizing the natural vacuum outside the earth""s atmosphere. Further objectives and advantages of my invention will become apparent from a consideration of the drawings and ensuing description.
The invention discloses a vacuum casting unit and a gas permeable mold, both being equipped with uniform mounting, sealing, and filling features configured to register with their corresponding counterparts. When a ready to cast gas permeable mold is set-up in an activated vacuum casting unit, molten metal is introduced into said mold by gravity means from outside the vacuum chamber while the mold is subjected to vacuum pressure.
The vacuum casting unit consists of a vacuum tank with a means for connecting and controlling a vacuum device, and a top closure that when joined together form a vacuum chamber configured to accept a correspondingly configured gas permeable mold.
Features of the top closure include a flat sealing surface with an orifice, through which a sprue-forming device, in accordance with this invention, projects and extends a gas permeable mold""s sprue, and through which molten metal is introduced into the vacuumized gas permeable mold""s cavity by gravity means. The top closure further includes adjustable hanger devices that connect the gas permeable mold to the top closure and which provides the means to adjust the gas permeable mold""s sealing properties from outside the vacuum chamber by lowering or raising the mold up to form a tighter abutment between the sealing surfaces.
The invention discloses a sprue-forming device that when combined with a disposable foundry pattern and subsequently invested together as a unit forms a gas permeable mold in accordance with this invention. Said sprue-forming device furnishes uniform sprue, mounting, and sealing features for all sizes, shapes, and mold types pertinent to this invention. The preferred embodiment of said sprue-forming device forms a structural framework that surrounds the disposable foundry pattern and carries all the weight of the mold through every step of the foundry process. Said sprue-forming device is comprised of a sprue former ring, a base plate, and other structural elements such as tie wire and connecting rods or other suitable equivalents depending upon the amount of support required for a particular application. A sprue former ring is required to be sprued and invested as an integral part of all molds utilized in this process. The sprue-forming device may be structured to the most appropriate form conditional to the disposable foundry pattern and mold type being cast.
The sprue former ring is comprised of a sprue former flask a sealing surface, and mounting device all axially arranged and permanently fixed together. Said sprue former flask is a hollow metal cylinder, flanged at one end to form the sprue former ring""s sealing surface. Set-up of a sprue former ring to a disposable foundry pattern involves attaching a wax, or it""s equivalent, sprue pattern to the disposable foundry pattern. Said wax sprue pattern is long enough to extend concentrically all the way through the sprue former flask where it is invested in place. After burning out the mold, a sprue is left through the investment that now lines the sprue former flask and through which, molten metal gravity flows into the mold cavity during casting. The exterior surface of the sprue former flask and its associated sealing surface must be kept clean and free of investment before setting the mold up in the vacuum chamber in order for the sprue former flask to slip freely through the top closure""s center hole and to allow tight contact between sealing surfaces.
The aforementioned base plate, when used as part of a sprue-forming device, is positioned at the opposite end from the sprue former ring and held in place by connecting rods secured by winding tie wire around each juncture of a connecting rod with a base plate anchor bar and sprue former ring. The base plate includes a handle mount and a concentrically located drain port. A handle may be threaded into said handle mount to provide for convenient handling of unwieldy molds. The drain port serves two functions. First, it provides alignment for a wax coated sprue pipe when the disposable foundry pattern is sprued, and secondly, during the pattern elimination phase it provides a conduit for melting pattern material to flow out of the mold cavity. Alignment of the sprue pipe with the base plate is assured by threading an alignment plug through the drain port. The alignment plug is a long bolt that is threaded for part of its length and smoothed to a smaller diameter for the remainder of its length. The outside diameter of the smooth part of the alignment plug allows that portion of the alignment plug to slip fit into the inside of the wax coated sprue pipe holding it firmly in place until investing is complete. After investing is complete, and when the investment is thoroughly dry, the alignment plug is removed to facilitate pattern elimination. After burnout and before setting the gas permeable mold up in the vacuum chamber a drain plug must be threaded into the drain port to seal the mold cavity.
While the invention is described in connection with certain described embodiments and applications, it will be understood that it is not intended to limit the invention to these particular descriptions or uses. On the contrary, it is intended to cover all alternatives, modifications, and equivalent arrangements as may be included within the scope of this invention.